1. Field of the Invention
This invention relates to a method of finishing an X-ray mirror for use in such as an X-ray microscope and an apparatus for manufacturing the same finished X-ray mirror.
2. Description of the Related Art
X-rays have the features that their wavelength are longer than those of visible light and their transmission power is larger than that of electron beams. Since the X-ray has an absorption wavelength band inherent to each element, it is possible to identify a specified element through the utilization of the aforementioned nature of the X-ray as well as a fluorescent X-ray. For this reason, the X-rays provide an important means capable of obtaining atomic level information relating to an object.
However, in the wavelength range of the X-ray, the refractive index of an object is very approximate to unity. Accordingly, it was very difficult to manufacture lenses and mirrors for X-rays, which have the same functions as that of a refractive lens and a direct incident type reflecting mirror used in the visible region.
A recently developed X-ray microscope uses an X-ray mirror utilizing such a nature in which the X-rays are totally reflected when they are incident on a reflecting mirror surface at a very large angle of incident, that is, at a very small angle made with the reflecting mirror surface. An X-ray mirror having a Wolter-type reflecting mirror surface is well known. This mirror is formed in a substantially cylindrical shape, and its inner surface constitutes a hyperboloid of revolution and a reflecting surface of an ellipsoidal surface of revolution continuous thereto. These reflecting surfaces have a common focal point F1. With this mirror, a focal point F2 is selected as the object point, and the X-rays passing the object point are reflected by these two reflecting surfaces to be focused on a focal point F3. The use of the two reflecting surfaces reduces the distortion of the image of the object point which departs from the optical axis.
When an X-ray mirror having the above structure is applied to an X-ray microscope, light shielding plates are provided at the opening portions at both ends of the X-ray mirror such that X-rays reflected by the two reflecting surfaces are imaged on a detector located on the focal point F3. The light shielding plates are adapted to shield that X-rays of an X-ray beam shade the rays directly directed to the detector without emerging from the object point which are directed toward the detector without being incident on the reflecting surfaces. The X-rays enter the mirror through an annular slit defined between the peripheral edge of one of the shielding plates and one of the opening edges of the mirror and leave the mirror through an annular slit defined between the peripheral edge of the other shielding plate and the other opening edge of the mirror. It is required that these slits be coaxially arranged with the center axis of the X-ray mirror at the tolerance of several micrometers to several tens of micrometers.
Generally, the resolving ability of an X-ray microscope is determined by the finishing accuracy of reflecting surfaces which form the surfaces of revolution. The finishing accuracy of a reflecting mirror is classed as a surface roughness close to the wavelengths of the X-ray and a form accuracy having a relatively large period. In order to visualize an ideal X-ray microscope, it is required that the accuracy of processing the surface roughness of the reflecting surfaces should be in the order of nm or less. When the form accuracy is 0.07 micrometer and the surface roughness is 6 nm, for example, it is found that the resolving ability of the X-ray microscope is 0.1 micrometer.
However, it was very difficult to process, at accuracy in the order of nm or higher accuracy hyperboloid of revolution and an ellipsoid of revolution which are aspherical, and the required accuracy could not be attained by the conventional technique.